The parent class for all constructed encodings. The value attribute of a Constructive is always an Array. Attributes are the same as for ASN1Data, with the addition of tagging.


Most constructed encodings come in the form of a SET or a SEQUENCE. These encodings are represented by one of the two sub-classes of Constructive:

  • OpenSSL::ASN1::Set

  • OpenSSL::ASN1::Sequence

Please note that tagged sequences and sets are still parsed as instances of ASN1Data. Find further details on tagged values there.

Example - constructing a SEQUENCE

int =
str ='abc')
sequence = [ int, str ] )

Example - constructing a SET

int =
str ='abc')
set = [ int, str ] )

Infinite length primitive values

The only case where Constructive is used directly is for infinite length encodings of primitive values. These encodings are always constructed, with the contents of the value Array being either UNIVERSAL non-infinite length partial encodings of the actual value or again constructive encodings with infinite length (i.e. infinite length primitive encodings may be constructed recursively with another infinite length value within an already infinite length value). Each partial encoding must be of the same UNIVERSAL type as the overall encoding. The value of the overall encoding consists of the concatenation of each partial encoding taken in sequence. The value array of the outer infinite length value must end with a OpenSSL::ASN1::EndOfContent instance.

Please note that it is not possible to encode Constructive without the infinite_length attribute being set to true, use OpenSSL::ASN1::Sequence or OpenSSL::ASN1::Set in these cases instead.

Example - Infinite length OCTET STRING

partial1 ="\x01")
partial2 ="\x02")
inf_octets = [ partial1,
                                              :UNIVERSAL )
# The real value of inf_octets is "\x01\x02", i.e. the concatenation
# of partial1 and partial2
inf_octets.infinite_length = true
der = inf_octets.to_der
asn1 = OpenSSL::ASN1.decode(der)
puts asn1.infinite_length # => true
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